The long term goal of this developmental project is improve the treatment of myasthenia gravis (MG) and, possibly, other antibody (Ab)-mediated autoimmune diseases, by specifically targeting the autoimmune process, with little or no effect on the normal functioning of the immune system. We will make use of syngeneic chimeric autoantibody receptor (CAAR)- expressing T cells (CAART) to attack autoAb-producing B cells in the rat model of muscle- specific kinase (MuSK)-MG, experimental autoimmune MuSK myasthenia (EAMM). CAART are modeled after chimeric antigen receptor (CAR) T cells (CART) that express an engineered CAR to target tumor cells, by employing the single chain Fv of an anti-tumor Ab fused to the T cell receptor framework. For CAAR, the single chain anti-tumor Fv is replaced by the autoantigen, in this case, MuSK ectodomain, to target the anti-MuSK Ab displayed on the surface of the autoimmune B cells. The previous use of CAART has involved a chimeric human/mouse animal model of pemphigus vulgaris (PV) in immunodeficient mice. The current autoimmune model better approximates human autoimmune disease in that it is induced by active immunization of an immunocompetent host. The Specific Aims are: 1) assess, and optimize, in vitro the ability of rat MuSK CAART to reduce/eliminate syngeneic anti-MuSK B cells and MuSK Ab secretion; 2) assess the ability of injected syngeneic MuSK CAART to prevent and treat EAMM, as well as screening for off-target and other adverse effects. cDNA coding the autoantigen will be inserted into a lentiviral vector that has been effective in transfecting human T cells to produce human PV CAART. In preliminary EAMM studies, this vector has successfully transduced rat T cells as well. For the in vitro experiments, two types of autoimmune B cells will be used as targets for the CAART: anti-MuSK hybridomas and polyclonal anti-MuSK B cells isolated from spleens of MuSK-immunized rats. Assays for CAART efficacy will include measures of in vitro B cell killing: Cr release and reduced MuSK Ab-secreting B cells in an ELISPOT. In terms of in vivo treatment of EAMM, dose-finding experiments will be carried out by assessing disease severity clinically, electrophysiologically and by morphometric analysis of the neuromuscular synapse, the target structure in MG. Potential adverse effects of injected CAART will be monitored assessing neuromuscular junction structure and function, cytokine levels, blood chemistries and blood counts and by necropsy screen of various organs.